This invention relates to a refractory powder flame projecting apparatus, and more particularly to an apparatus for projecting fused or semi-fused refractory powder to deposit refractory buildup for the purpose of repairing the worn or eroded portion of furnace refractory lining, manufacturing refractory brick, or building furnaces.
Furnaces and their auxiliary facilities used in the steel industry are mostly lined with refractory brick. With the passage of time, however, the refractory brick lining progressively wears or erodes down, either chemically attacked by high-temperature gases or slag or due to mechanical abrasion. When a certain time has passed, therefore, they are relined either totally or only in the damaged portions.
Conventionally, the repair is commonly accomplished by a technique known as the wet method, which comprises spraying powder material mixed with water. But this method has the following drawbacks:
(1) Refractory powder mixed with a small quantity of water does not adhere strongly to the sprayed areas, resulting in a great refractory loss.
(2) On spraying such a wet refractory mass onto furnace walls at high temperature, the water contained in the mixture evaporates quickly causing the refractory to form a porous, low-strength layer. When a binder or a flux is added to the mixture, the sprayed layer often becomes detached before attaining adequate sintered strength due to decomposition.
(3) Spraying the wet refractory mass onto hot furnace walls causes a sharp temperature drop, which in turn gives rise to spalling.
For these reasons, the wet-type relining technique is unable to form a refractory layer with good adhesiveness and high durability.
To eliminate the aforementioned shortcomings in the wet-type relining technique, several techniques to project refractory powder by flame have been proposed recently. The basic principle of these techniques is similar to that of a conventional practice popularly employed for applying ceramic coating on a metal surface and so on. But these flame projecting techniques can hardly be used for furnace relining and other similar purposes because of difficulties concerning the projecting capacities, workers safety, and properties of the formed refractory layer. Some techniques (such as one described in "Schweissen von Kokskammern und Glashafen mit Keramik Pulvern," Silikatechnik 21 (1970), No. 1, pp. 18-20) have been developed to overcome such difficulties which are also sought to be overcome by this invention. But none of them can form a dense, durable refractory layer. Besides the structure of the equipment they use is unsuitable for the relining of furnaces from the standpoint of projecting efficiency and safety.